The screams of his mother Parveen Ahmad were heard by two young girls, who ran up to passerby Ian Nurse and begged him to see what was wrong.

When Mr Nurse arrived on the doorstep of the family house, on a quiet road in a leafy Cardiff suburb opposite Roath Park, Aamir’s mother emerged, crying out the only words she could muster: “help” and “stab”.

Inside, Mr Nurse saw Aamir’s legs protruding into the hallway from a side room and he knelt beside the teenager’s body to check his pulse.

“There was nothing at all,” he later told Swansea Crown Court.

Minutes later, DS Stuart Wales, a senior detective who had heard the call for help on his police radio, arrived at the house.

Giving evidence in court, he described seeing Mrs Ahmad at the window.

“The net curtain of the window flung back and I didn’t expect it to,” he said.

“I looked to the right and I saw the face of Aamir’s mum, she looked absolutely traumatised. It’s still an image quite clear in my mind.”

Minutes before Ben Hope, 39, and Jason Richards, 38, knocked on the door of their family home, Mrs Ahmad told the court there had been a “happy atmosphere”.

She been expecting her son’s Koran teacher and, when she noticed someone at the door she thought it was the imam putting a square cloth on his shoulder.

“I did not realise it could be a mask,” she said.

Aamir, she said, was a loving son who always wanted to please her and so she asked him to open the door for the imam.

It was a decision that haunts her even now.

In an emotional statement to the court, she said: “I so regret now saying it was the imam.”

When Aamir answered the door, Hope and Richards immediately attacked.

Aamir’s father, Iqbal Ahmad, described how the pair made animalistic “howling” noises as they stabbed his son multiple times in the torso.

During a video interview which was played in court, Mr Ahmad, said: “As soon as the door opened, they attacked.”

Both parents were stabbed in the chest, head and arms as they fought to protect their son.

Mr Ahmad, who had undergone a knee replacement operation not long before the attack, told how he used all his energy to take hold of one of the pair’s hands and pin him against a wall with his head against his chest.

However, he said the man was too strong for him and slashed him twice before running off.

Meanwhile his wife, Parveen, jumped on the back of the other attacker who had chased Aamir into the dining room.

Hope and Richards ran away and, unable to make her phone work, Mrs Ahmad ran out into the street screaming at passersby to call for help.

When DS Wales arrived minutes later, he said it was “without doubt” the most difficult incident in which he had needed to make operational police decisions.

Next: 'Life has become very empty', says broken-hearted dad

“I’ve 17 years of police service and there’s no doubt about it, it was the most distressing incident I’ve ever had to attend,” said DS Wales.

“I’ve a lad of a similar age and it was quite close to home.”

He said he had “never heard anything like” the screaming coming from inside the house.

“It was terrible screaming.”

When he and others realised Mrs Ahmad’s condition was deteriorating, they made the heartrending decision to take her away from the house where she could get medical help.

DS Wales told the court: “Parveen was quite reluctant to leave the house. She could see what was going on in the hallway [where attempts were being made to resuscitate Aamir] and for obvious reasons she did not want to leave.”

Attempts were made to save Aamir’s life but he was pronounced dead at the University Hospital of Wales.

In the days and weeks that followed, his parents, three sisters and extended family and friends made repeated appeals to the public for help to find their “precious” boy’s killers.

With her parents at first too distraught to speak publicly, Aamir’s sister Nishat, 34, stepped in to tell a press conference at Cardiff Central police station that her little brother was “a friend” and “something precious that we will miss”.

A family friend re-read her statement in Urdu, with police hoping that members of the Hindu community would have information that could help.

That information quickly flooded in and, the very next day, Hope and Richards were arrested.

As the days passed, another arrest came and a series of businesses and private homes across the city were cordoned off by police as they searched for clues.

As officers supported Aamir’s grieving family, their colleagues combed their house and the street outside for clues. In court the jury was told the thousands of CCTV clips analysed by police would – if watched back-to-back – take days to get through.

Seventeen days after his murder, and after multiple appeals by Aamir’s family, the team of detectives working on the case made a breakthrough – a Drunk Punk top was found by on the Taff embankment containing DNA that would prove vital in the case against Hope and Richards.

But for the family, any sense of closure was still a long way away.

In a video interview played in court more than 17 months after his son’s brutal murder, Mr Ahmad cried as he attempted to put into words the impact it had made on their lives.

“Emotionally, we have been devastated,” he said, adding that the incident was enough to make a person mad.

He said Aamir’s death had “completely reshaped” their lives.

Their three daughters – born more than a decade before their brother – and all the plans they made years ago “centred on Aamir”, he said.

“Once he had gone, we were in a very difficult position.”

He explained that he is retired and added: “Life has become very empty. All we were doing was for Aamir.

“Life has lost its purpose. It has made us very unsettled and unhappy, we are trying to come to terms with it.”

For Mrs Ahmad, a play development worker with the council, the pain is still just as raw.

Describing her son as “an extraordinary person”, she told the court the moment of his death would live with her “all of my life”.

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